git.sesse.net Git - nageru/blob - flow.cpp

   1 #define NO_SDL_GLEXT 1
   2
   3 #define WIDTH 1280
   4 #define HEIGHT 720
   5
   6 #include <epoxy/gl.h>
   7
   8 #include <SDL2/SDL.h>
   9 #include <SDL2/SDL_error.h>
  10 #include <SDL2/SDL_events.h>
  11 #include <SDL2/SDL_image.h>
  12 #include <SDL2/SDL_keyboard.h>
  13 #include <SDL2/SDL_mouse.h>
  14 #include <SDL2/SDL_video.h>
  15
  16 #include <assert.h>
  17 #include <stdio.h>
  18
  19 #include <algorithm>
  20 #include <memory>
  21
  22 #define BUFFER_OFFSET(i) ((char *)nullptr + (i))
  23
  24 using namespace std;
  25
  26 // Operating point 3 (10 Hz on CPU, excluding preprocessing).
  27 constexpr float patch_overlap_ratio = 0.75f;
  28 constexpr unsigned coarsest_level = 5;
  29 constexpr unsigned finest_level = 1;
  30 constexpr unsigned patch_size_pixels = 12;
  31
  32 // Some global OpenGL objects.
  33 GLuint nearest_sampler, linear_sampler, mipmap_sampler;
  34 GLuint vertex_vbo;
  35
  36 string read_file(const string &filename)
  37 {
  38         FILE *fp = fopen(filename.c_str(), "r");
  39         if (fp == nullptr) {
  40                 perror(filename.c_str());
  41                 exit(1);
  42         }
  43
  44         int ret = fseek(fp, 0, SEEK_END);
  45         if (ret == -1) {
  46                 perror("fseek(SEEK_END)");
  47                 exit(1);
  48         }
  49
  50         int size = ftell(fp);
  51
  52         ret = fseek(fp, 0, SEEK_SET);
  53         if (ret == -1) {
  54                 perror("fseek(SEEK_SET)");
  55                 exit(1);
  56         }
  57
  58         string str;
  59         str.resize(size);
  60         ret = fread(&str[0], size, 1, fp);
  61         if (ret == -1) {
  62                 perror("fread");
  63                 exit(1);
  64         }
  65         if (ret == 0) {
  66                 fprintf(stderr, "Short read when trying to read %d bytes from %s\n",
  67                                 size, filename.c_str());
  68                 exit(1);
  69         }
  70         fclose(fp);
  71
  72         return str;
  73 }
  74
  75
  76 GLuint compile_shader(const string &shader_src, GLenum type)
  77 {
  78         GLuint obj = glCreateShader(type);
  79         const GLchar* source[] = { shader_src.data() };
  80         const GLint length[] = { (GLint)shader_src.size() };
  81         glShaderSource(obj, 1, source, length);
  82         glCompileShader(obj);
  83
  84         GLchar info_log[4096];
  85         GLsizei log_length = sizeof(info_log) - 1;
  86         glGetShaderInfoLog(obj, log_length, &log_length, info_log);
  87         info_log[log_length] = 0;
  88         if (strlen(info_log) > 0) {
  89                 fprintf(stderr, "Shader compile log: %s\n", info_log);
  90         }
  91
  92         GLint status;
  93         glGetShaderiv(obj, GL_COMPILE_STATUS, &status);
  94         if (status == GL_FALSE) {
  95                 // Add some line numbers to easier identify compile errors.
  96                 string src_with_lines = "/*   1 */ ";
  97                 size_t lineno = 1;
  98                 for (char ch : shader_src) {
  99                         src_with_lines.push_back(ch);
 100                         if (ch == '\n') {
 101                                 char buf[32];
 102                                 snprintf(buf, sizeof(buf), "/* %3zu */ ", ++lineno);
 103                                 src_with_lines += buf;
 104                         }
 105                 }
 106
 107                 fprintf(stderr, "Failed to compile shader:\n%s\n", src_with_lines.c_str());
 108                 exit(1);
 109         }
 110
 111         return obj;
 112 }
 113
 114
 115 GLuint load_texture(const char *filename, unsigned width, unsigned height)
 116 {
 117         FILE *fp = fopen(filename, "rb");
 118         if (fp == nullptr) {
 119                 perror(filename);
 120                 exit(1);
 121         }
 122         unique_ptr<uint8_t[]> pix(new uint8_t[width * height]);
 123         if (fread(pix.get(), width * height, 1, fp) != 1) {
 124                 fprintf(stderr, "Short read from %s\n", filename);
 125                 exit(1);
 126         }
 127         fclose(fp);
 128
 129         // Convert to bottom-left origin.
 130         for (unsigned y = 0; y < height / 2; ++y) {
 131                 unsigned y2 = height - 1 - y;
 132                 swap_ranges(&pix[y * width], &pix[y * width + width], &pix[y2 * width]);
 133         }
 134
 135         int levels = 1;
 136         for (int w = width, h = height; w > 1 || h > 1; ) {
 137                 w >>= 1;
 138                 h >>= 1;
 139                 ++levels;
 140         }
 141
 142         GLuint tex;
 143         glCreateTextures(GL_TEXTURE_2D, 1, &tex);
 144         glTextureStorage2D(tex, levels, GL_R8, width, height);
 145         glTextureSubImage2D(tex, 0, 0, 0, width, height, GL_RED, GL_UNSIGNED_BYTE, pix.get());
 146         glGenerateTextureMipmap(tex);
 147
 148         return tex;
 149 }
 150
 151 GLuint link_program(GLuint vs_obj, GLuint fs_obj)
 152 {
 153         GLuint program = glCreateProgram();
 154         glAttachShader(program, vs_obj);
 155         glAttachShader(program, fs_obj);
 156         glLinkProgram(program);
 157         GLint success;
 158         glGetProgramiv(program, GL_LINK_STATUS, &success);
 159         if (success == GL_FALSE) {
 160                 GLchar error_log[1024] = {0};
 161                 glGetProgramInfoLog(program, 1024, nullptr, error_log);
 162                 fprintf(stderr, "Error linking program: %s\n", error_log);
 163                 exit(1);
 164         }
 165         return program;
 166 }
 167
 168 GLuint generate_vbo(GLint size, GLsizeiptr data_size, const GLvoid *data)
 169 {
 170         GLuint vbo;
 171         glCreateBuffers(1, &vbo);
 172         glBufferData(GL_ARRAY_BUFFER, data_size, data, GL_STATIC_DRAW);
 173         glNamedBufferData(vbo, data_size, data, GL_STATIC_DRAW);
 174         return vbo;
 175 }
 176
 177 GLuint fill_vertex_attribute(GLuint vao, GLuint glsl_program_num, const string &attribute_name, GLint size, GLenum type, GLsizeiptr data_size, const GLvoid *data)
 178 {
 179         int attrib = glGetAttribLocation(glsl_program_num, attribute_name.c_str());
 180         if (attrib == -1) {
 181                 return -1;
 182         }
 183
 184         GLuint vbo = generate_vbo(size, data_size, data);
 185
 186         glBindBuffer(GL_ARRAY_BUFFER, vbo);
 187         glEnableVertexArrayAttrib(vao, attrib);
 188         glVertexAttribPointer(attrib, size, type, GL_FALSE, 0, BUFFER_OFFSET(0));
 189         glBindBuffer(GL_ARRAY_BUFFER, 0);
 190
 191         return vbo;
 192 }
 193
 194 void bind_sampler(GLuint program, const char *uniform_name, GLuint texture_unit, GLuint tex, GLuint sampler)
 195 {
 196         GLint location = glGetUniformLocation(program, uniform_name);
 197         if (location == -1) {
 198                 return;
 199         }
 200
 201         glBindTextureUnit(texture_unit, tex);
 202         glBindSampler(texture_unit, sampler);
 203         glProgramUniform1i(program, location, texture_unit);
 204 }
 205
 206 // Compute gradients in every point, used for the motion search.
 207 // The DIS paper doesn't actually mention how these are computed,
 208 // but seemingly, a 3x3 Sobel operator is used here (at least in
 209 // later versions of the code), while a [1 -8 0 8 -1] kernel is
 210 // used for all the derivatives in the variational refinement part
 211 // (which borrows code from DeepFlow). This is inconsistent,
 212 // but I guess we're better off with staying with the original
 213 // decisions until we actually know having different ones would be better.
 214 class Sobel {
 215 public:
 216         Sobel();
 217         void exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_height);
 218
 219 private:
 220         GLuint sobel_vs_obj;
 221         GLuint sobel_fs_obj;
 222         GLuint sobel_program;
 223         GLuint sobel_vao;
 224 };
 225
 226 Sobel::Sobel()
 227 {
 228         sobel_vs_obj = compile_shader(read_file("vs.vert"), GL_VERTEX_SHADER);
 229         sobel_fs_obj = compile_shader(read_file("sobel.frag"), GL_FRAGMENT_SHADER);
 230         sobel_program = link_program(sobel_vs_obj, sobel_fs_obj);
 231
 232         // Set up the VAO containing all the required position/texcoord data.
 233         glCreateVertexArrays(1, &sobel_vao);
 234         glBindVertexArray(sobel_vao);
 235
 236         GLint position_attrib = glGetAttribLocation(sobel_program, "position");
 237         glEnableVertexArrayAttrib(sobel_vao, position_attrib);
 238         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 239
 240         GLint texcoord_attrib = glGetAttribLocation(sobel_program, "texcoord");
 241         glEnableVertexArrayAttrib(sobel_vao, texcoord_attrib);
 242         glVertexAttribPointer(texcoord_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 243 }
 244
 245 void Sobel::exec(GLint tex0_view, GLint grad0_tex, int level_width, int level_height)
 246 {
 247         glUseProgram(sobel_program);
 248         glBindTextureUnit(0, tex0_view);
 249         glBindSampler(0, nearest_sampler);
 250         glProgramUniform1i(sobel_program, glGetUniformLocation(sobel_program, "tex"), 0);
 251         glProgramUniform2f(sobel_program, glGetUniformLocation(sobel_program, "image_size"), level_width, level_height);
 252         glProgramUniform2f(sobel_program, glGetUniformLocation(sobel_program, "inv_image_size"), 1.0f / level_width, 1.0f / level_height);
 253
 254         GLuint grad0_fbo;  // TODO: cleanup
 255         glCreateFramebuffers(1, &grad0_fbo);
 256         glNamedFramebufferTexture(grad0_fbo, GL_COLOR_ATTACHMENT0, grad0_tex, 0);
 257
 258         glViewport(0, 0, level_width, level_height);
 259         glBindFramebuffer(GL_FRAMEBUFFER, grad0_fbo);
 260         glBindVertexArray(sobel_vao);
 261         glUseProgram(sobel_program);
 262         glDisable(GL_BLEND);
 263         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 264 }
 265
 266 // Motion search to find the initial flow. See motion_search.frag for documentation.
 267 class MotionSearch {
 268 public:
 269         MotionSearch();
 270         void exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GLuint flow_tex, GLuint flow_out_tex, int level_width, int level_height, int width_patches, int height_patches);
 271
 272 private:
 273         GLuint motion_vs_obj;
 274         GLuint motion_fs_obj;
 275         GLuint motion_search_program;
 276         GLuint motion_search_vao;
 277 };
 278
 279 MotionSearch::MotionSearch()
 280 {
 281         motion_vs_obj = compile_shader(read_file("motion_search.vert"), GL_VERTEX_SHADER);
 282         motion_fs_obj = compile_shader(read_file("motion_search.frag"), GL_FRAGMENT_SHADER);
 283         motion_search_program = link_program(motion_vs_obj, motion_fs_obj);
 284
 285         // Set up the VAO containing all the required position/texcoord data.
 286         glCreateVertexArrays(1, &motion_search_vao);
 287         glBindVertexArray(motion_search_vao);
 288         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 289
 290         GLint position_attrib = glGetAttribLocation(motion_search_program, "position");
 291         glEnableVertexArrayAttrib(motion_search_vao, position_attrib);
 292         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 293
 294         GLint texcoord_attrib = glGetAttribLocation(motion_search_program, "texcoord");
 295         glEnableVertexArrayAttrib(motion_search_vao, texcoord_attrib);
 296         glVertexAttribPointer(texcoord_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 297 }
 298
 299 void MotionSearch::exec(GLuint tex0_view, GLuint tex1_view, GLuint grad0_tex, GLuint flow_tex, GLuint flow_out_tex, int level_width, int level_height, int width_patches, int height_patches)
 300 {
 301         glUseProgram(motion_search_program);
 302
 303         bind_sampler(motion_search_program, "image0_tex", 0, tex0_view, nearest_sampler);
 304         bind_sampler(motion_search_program, "image1_tex", 1, tex1_view, linear_sampler);
 305         bind_sampler(motion_search_program, "grad0_tex", 2, grad0_tex, nearest_sampler);
 306         bind_sampler(motion_search_program, "flow_tex", 3, flow_tex, linear_sampler);
 307
 308         glProgramUniform2f(motion_search_program, glGetUniformLocation(motion_search_program, "image_size"), level_width, level_height);
 309         glProgramUniform2f(motion_search_program, glGetUniformLocation(motion_search_program, "inv_image_size"), 1.0f / level_width, 1.0f / level_height);
 310
 311         GLuint flow_fbo;  // TODO: cleanup
 312         glCreateFramebuffers(1, &flow_fbo);
 313         glNamedFramebufferTexture(flow_fbo, GL_COLOR_ATTACHMENT0, flow_out_tex, 0);
 314
 315         glViewport(0, 0, width_patches, height_patches);
 316         glBindFramebuffer(GL_FRAMEBUFFER, flow_fbo);
 317         glBindVertexArray(motion_search_vao);
 318         glUseProgram(motion_search_program);
 319         glDrawArrays(GL_TRIANGLE_STRIP, 0, 4);
 320 }
 321
 322 // Do “densification”, ie., upsampling of the flow patches to the flow field
 323 // (the same size as the image at this level). We draw one quad per patch
 324 // over its entire covered area (using instancing in the vertex shader),
 325 // and then weight the contributions in the pixel shader by post-warp difference.
 326 // This is equation (3) in the paper.
 327 //
 328 // We accumulate the flow vectors in the R/G channels (for u/v) and the total
 329 // weight in the B channel. Dividing R and G by B gives the normalized values.
 330 class Densify {
 331 public:
 332         Densify();
 333         void exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint dense_flow_tex, int level_width, int level_height, int width_patches, int height_patches);
 334
 335 private:
 336         GLuint densify_vs_obj;
 337         GLuint densify_fs_obj;
 338         GLuint densify_program;
 339         GLuint densify_vao;
 340 };
 341
 342 Densify::Densify()
 343 {
 344         densify_vs_obj = compile_shader(read_file("densify.vert"), GL_VERTEX_SHADER);
 345         densify_fs_obj = compile_shader(read_file("densify.frag"), GL_FRAGMENT_SHADER);
 346         densify_program = link_program(densify_vs_obj, densify_fs_obj);
 347
 348         // Set up the VAO containing all the required position/texcoord data.
 349         glCreateVertexArrays(1, &densify_vao);
 350         glBindVertexArray(densify_vao);
 351         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 352
 353         GLint position_attrib = glGetAttribLocation(densify_program, "position");
 354         glEnableVertexArrayAttrib(densify_vao, position_attrib);
 355         glVertexAttribPointer(position_attrib, 2, GL_FLOAT, GL_FALSE, 0, BUFFER_OFFSET(0));
 356 }
 357
 358 void Densify::exec(GLuint tex0_view, GLuint tex1_view, GLuint flow_tex, GLuint dense_flow_tex, int level_width, int level_height, int width_patches, int height_patches)
 359 {
 360         glUseProgram(densify_program);
 361
 362         bind_sampler(densify_program, "image0_tex", 0, tex0_view, nearest_sampler);
 363         bind_sampler(densify_program, "image1_tex", 1, tex1_view, linear_sampler);
 364         bind_sampler(densify_program, "flow_tex", 2, flow_tex, nearest_sampler);
 365
 366         glProgramUniform1i(densify_program, glGetUniformLocation(densify_program, "width_patches"), width_patches);
 367         glProgramUniform2f(densify_program, glGetUniformLocation(densify_program, "patch_size"),
 368                 float(patch_size_pixels) / level_width,
 369                 float(patch_size_pixels) / level_height);
 370
 371         float patch_spacing_x = float(level_width - patch_size_pixels) / (width_patches - 1);
 372         float patch_spacing_y = float(level_height - patch_size_pixels) / (height_patches - 1);
 373         glProgramUniform2f(densify_program, glGetUniformLocation(densify_program, "patch_spacing"),
 374                 patch_spacing_x / level_width,
 375                 patch_spacing_y / level_height);
 376
 377         GLuint dense_flow_fbo;  // TODO: cleanup
 378         glCreateFramebuffers(1, &dense_flow_fbo);
 379         glNamedFramebufferTexture(dense_flow_fbo, GL_COLOR_ATTACHMENT0, dense_flow_tex, 0);
 380
 381         glViewport(0, 0, level_width, level_height);
 382         glEnable(GL_BLEND);
 383         glBlendFunc(GL_ONE, GL_ONE);
 384         glBindVertexArray(densify_vao);
 385         glBindFramebuffer(GL_FRAMEBUFFER, dense_flow_fbo);
 386         glDrawArraysInstanced(GL_TRIANGLE_STRIP, 0, 4, width_patches * height_patches);
 387 }
 388
 389 int main(void)
 390 {
 391         if (SDL_Init(SDL_INIT_EVERYTHING) == -1) {
 392                 fprintf(stderr, "SDL_Init failed: %s\n", SDL_GetError());
 393                 exit(1);
 394         }
 395         SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE, 8);
 396         SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE, 0);
 397         SDL_GL_SetAttribute(SDL_GL_STENCIL_SIZE, 0);
 398         SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER, 1);
 399
 400         SDL_GL_SetAttribute(SDL_GL_CONTEXT_PROFILE_MASK, SDL_GL_CONTEXT_PROFILE_CORE);
 401         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MAJOR_VERSION, 4);
 402         SDL_GL_SetAttribute(SDL_GL_CONTEXT_MINOR_VERSION, 5);
 403         // SDL_GL_SetAttribute(SDL_GL_CONTEXT_FLAGS, SDL_GL_CONTEXT_DEBUG_FLAG);
 404         SDL_Window *window = SDL_CreateWindow("OpenGL window",
 405                         SDL_WINDOWPOS_UNDEFINED,
 406                         SDL_WINDOWPOS_UNDEFINED,
 407                         64, 64,
 408                         SDL_WINDOW_OPENGL);
 409         SDL_GLContext context = SDL_GL_CreateContext(window);
 410         assert(context != nullptr);
 411
 412         // Load pictures.
 413         GLuint tex0 = load_texture("test1499.pgm", WIDTH, HEIGHT);
 414         GLuint tex1 = load_texture("test1500.pgm", WIDTH, HEIGHT);
 415
 416         // Make some samplers.
 417         glCreateSamplers(1, &nearest_sampler);
 418         glSamplerParameteri(nearest_sampler, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
 419         glSamplerParameteri(nearest_sampler, GL_TEXTURE_MAG_FILTER, GL_NEAREST);
 420         glSamplerParameteri(nearest_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 421         glSamplerParameteri(nearest_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 422
 423         glCreateSamplers(1, &linear_sampler);
 424         glSamplerParameteri(linear_sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
 425         glSamplerParameteri(linear_sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 426         glSamplerParameteri(linear_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 427         glSamplerParameteri(linear_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 428
 429         glCreateSamplers(1, &mipmap_sampler);
 430         glSamplerParameteri(mipmap_sampler, GL_TEXTURE_MIN_FILTER, GL_LINEAR_MIPMAP_NEAREST);
 431         glSamplerParameteri(mipmap_sampler, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
 432         glSamplerParameteri(mipmap_sampler, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
 433         glSamplerParameteri(mipmap_sampler, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
 434
 435         float vertices[] = {
 436                 0.0f, 1.0f,
 437                 0.0f, 0.0f,
 438                 1.0f, 1.0f,
 439                 1.0f, 0.0f,
 440         };
 441         glCreateBuffers(1, &vertex_vbo);
 442         glNamedBufferData(vertex_vbo, sizeof(vertices), vertices, GL_STATIC_DRAW);
 443         glBindBuffer(GL_ARRAY_BUFFER, vertex_vbo);
 444
 445         // Initial flow is zero, 1x1.
 446         GLuint initial_flow_tex;
 447         glCreateTextures(GL_TEXTURE_2D, 1, &initial_flow_tex);
 448         glTextureStorage2D(initial_flow_tex, 1, GL_RGB32F, 1, 1);
 449
 450         GLuint prev_level_flow_tex = initial_flow_tex;
 451
 452         Sobel sobel;
 453         MotionSearch motion_search;
 454         Densify densify;
 455
 456         for (int level = coarsest_level; level >= int(finest_level); --level) {
 457                 int level_width = WIDTH >> level;
 458                 int level_height = HEIGHT >> level;
 459                 float patch_spacing_pixels = patch_size_pixels * (1.0f - patch_overlap_ratio);
 460                 int width_patches = 1 + lrintf((level_width - patch_size_pixels) / patch_spacing_pixels);
 461                 int height_patches = 1 + lrintf((level_height - patch_size_pixels) / patch_spacing_pixels);
 462
 463                 // Make sure we always read from the correct level; the chosen
 464                 // mipmapping could otherwise be rather unpredictable, especially
 465                 // during motion search.
 466                 // TODO: create these beforehand, and stop leaking them.
 467                 GLuint tex0_view, tex1_view;
 468                 glGenTextures(1, &tex0_view);
 469                 glTextureView(tex0_view, GL_TEXTURE_2D, tex0, GL_R8, level, 1, 0, 1);
 470                 glGenTextures(1, &tex1_view);
 471                 glTextureView(tex1_view, GL_TEXTURE_2D, tex1, GL_R8, level, 1, 0, 1);
 472
 473                 // Create a new texture; we could be fancy and render use a multi-level
 474                 // texture, but meh.
 475                 GLuint grad0_tex;
 476                 glCreateTextures(GL_TEXTURE_2D, 1, &grad0_tex);
 477                 glTextureStorage2D(grad0_tex, 1, GL_RG16F, level_width, level_height);
 478
 479                 // Find the derivative.
 480                 sobel.exec(tex0_view, grad0_tex, level_width, level_height);
 481
 482                 // Motion search to find the initial flow. We use the flow from the previous
 483                 // level (sampled bilinearly; no fancy tricks) as a guide, then search from there.
 484
 485                 // Create an output flow texture.
 486                 GLuint flow_out_tex;
 487                 glCreateTextures(GL_TEXTURE_2D, 1, &flow_out_tex);
 488                 glTextureStorage2D(flow_out_tex, 1, GL_RG16F, width_patches, height_patches);
 489
 490                 // And draw.
 491                 motion_search.exec(tex0_view, tex1_view, grad0_tex, prev_level_flow_tex, flow_out_tex, level_width, level_height, width_patches, height_patches);
 492
 493                 // Densification.
 494
 495                 // Set up an output texture.
 496                 GLuint dense_flow_tex;
 497                 glCreateTextures(GL_TEXTURE_2D, 1, &dense_flow_tex);
 498                 //glTextureStorage2D(dense_flow_tex, 1, GL_RGB16F, level_width, level_height);
 499                 glTextureStorage2D(dense_flow_tex, 1, GL_RGBA32F, level_width, level_height);
 500
 501                 // And draw.
 502                 densify.exec(tex0_view, tex1_view, flow_out_tex, dense_flow_tex, level_width, level_height, width_patches, height_patches);
 503
 504                 // TODO: Variational refinement.
 505
 506                 prev_level_flow_tex = dense_flow_tex;
 507         }
 508
 509         int level_width = WIDTH >> finest_level;
 510         int level_height = HEIGHT >> finest_level;
 511         unique_ptr<float[]> dense_flow(new float[level_width * level_height * 3]);
 512         glGetTextureImage(prev_level_flow_tex, 0, GL_RGB, GL_FLOAT, level_width * level_height * 3 * sizeof(float), dense_flow.get());
 513
 514         FILE *fp = fopen("flow.ppm", "wb");
 515         fprintf(fp, "P6\n%d %d\n255\n", level_width, level_height);
 516         for (unsigned y = 0; y < unsigned(level_height); ++y) {
 517                 int yy = level_height - y - 1;
 518                 for (unsigned x = 0; x < unsigned(level_width); ++x) {
 519                         float du = dense_flow[(yy * level_width + x) * 3 + 0];
 520                         float dv = dense_flow[(yy * level_width + x) * 3 + 1];
 521                         float w = dense_flow[(yy * level_width + x) * 3 + 2];
 522
 523                         du /= w;
 524                         dv /= w;
 525
 526                         float angle = atan2(dv * level_width, du * level_height);
 527                         float magnitude = min(hypot(du * level_width, dv * level_height) / 20.0, 1.0);
 528
 529                         // HSV to RGB (from Wikipedia). Saturation is 1.
 530                         float c = magnitude;
 531                         float h = (angle + M_PI) * 6.0 / (2.0 * M_PI);
 532                         float X = c * (1.0 - fabs(fmod(h, 2.0) - 1.0));
 533                         float r = 0.0f, g = 0.0f, b = 0.0f;
 534                         if (h < 1.0f) {
 535                                 r = c; g = X;
 536                         } else if (h < 2.0f) {
 537                                 r = X; g = c;
 538                         } else if (h < 3.0f) {
 539                                 g = c; b = X;
 540                         } else if (h < 4.0f) {
 541                                 g = X; b = c;
 542                         } else if (h < 5.0f) {
 543                                 r = X; b = c;
 544                         } else if (h < 6.0f) {
 545                                 r = c; b = X;
 546                         } else {
 547                                 // h is NaN, so black is fine.
 548                         }
 549                         float m = magnitude - c;
 550                         r += m; g += m; b += m;
 551                         r = max(min(r, 1.0f), 0.0f);
 552                         g = max(min(g, 1.0f), 0.0f);
 553                         b = max(min(b, 1.0f), 0.0f);
 554                         putc(lrintf(r * 255.0f), fp);
 555                         putc(lrintf(g * 255.0f), fp);
 556                         putc(lrintf(b * 255.0f), fp);
 557                 }
 558         }
 559         fclose(fp);
 560
 561         fprintf(stderr, "err = %d\n", glGetError());
 562 }